In some elevator installations, at least one safety system is provided to combat uncontrolled vertical movements of a load receiving means or a counterweight of the elevator installation.
The safety system comprises at least one safety brake device with brake equipment which can be brought into an activated, braking state and a deactivated, non-braking state, wherein the safety brake device in the activated state connects the load receiving means with a guide rail by friction couple. The non-braking state of the brake equipment is also termed normal operating state. In addition, the safety system comprises at least one activating mechanism activating the brake equipment.
Such safety systems, which function exclusively mechanically, are widespread. In that case use is made of a limiter cable which is guided in the upper region of the elevator shaft around the cable pulley of a speed limiter and in the lower region around a deflecting cable pulley, wherein one of the runs of the limiter cable extending between these cable pulleys is coupled with an activating mechanism of the safety brake device at the load receiving means. The movements of the load receiving means or the counterweight are thereby transmitted by way of the limiter cable to the cable pulley at the speed limiter so that in the case of movement of the load receiving means or the counterweight this cable pulley executes a rotational movement, the rotational speed of which is proportional to the travel speed of the load receiving means. The speed limiter functions so that when an impermissibly high speed of the receiving means or the counterweight occurs the cable pulley of the speed limiter is blocked or a cable brake of the speed limited is activated. The limiter cable and thus the run of the limiter cable moving synchronously with the load receiving means or the counterweight are thereby stopped. This has the consequence that the stationary limiter cable activates the activating mechanism of the safety brake, which is mounted on the still-moving load receiving means or counterweight, and the load receiving means is brought to a standstill.
For the sake of simplicity not only load receiving means such as, for example, elevator cages, but also counterweights are to be understood in the following by the term “load receiving means”.
A potential disadvantage of such safety systems with speed limiters and limiter cables is, apart from the high constructional cost, that they do not do adequate justice to the demands of elevator installations without an engine room. Thus, the omission of the engine room can mean that an unrestricted capability of access to the speed limiter is not guaranteed.
Safety systems in which activation of the safety brake device takes place electromechanically are on the market to an increasing extent. Detection of excess speed is carried out electronically. Such safety systems dispense with a purely mechanical speed limiter, thus a limiter functioning even in the case of power failure. An emergency power battery or accumulator is usually provided in such safety systems for the case of a power failure.